Undergrad Special relativity and sameness

[Vadim Matveev]

Bartalomeo is absolutely right.
Let us consider a long rod, supplied with literal marks and having approximately such form:

B C D F G H J K L M N P Q R S T V W X Z​

Assume that the rod is made from combustible material and, after simultaneous ignition of its ends in a reference frame K, where the rod is at rest, is gradually and symmetrically burning from two ends. At a certain moment in time in this frame of reference K the processes of burning reach the marks D and W of the rod (simultaneously on the clocks of the inertial frame K), and the burning rod takes the form

*D F G H J K L M N P Q R S T V W*​

The signs * at the ends of the rod symbolize here the burning of the rod from two sides.
Let us name the short-term existing burning rod remainder burned to the marks D and W and continuing to burn as remainder *DW*, using for its designation literal marks of the remainder ends burning at the given instant and the signs *. This designation makes it possible to distinguish different concrete remainders of the “same” rod, for example the remainder *CX*, existed at a certain moment t₁, and the remainder *DW*, which exists at the moment t₂. The remainder *CX* and the remainder *DW* - are different physical objects, which have different lengths and masses (and different numbers of molecules).
Let us imagine now that the remainder of the burning rod with a high longitudinal velocity v flies past the observers of an inertial frame of reference Kʹ. Assume that at a certain moment in this frame of reference Kʹ the processes of burning reach the marks D and R of the rod (simultaneously on the clocks of the inertial frame Kʹ). The remainder *DR* looks at this moment like:

*DFGHJKLMNPQR*​

So! The remainders *DW* and *DR* are different remainders of the “same” rod. The remainders *DW* and *DR* are different physical objects. They have different numbers of molecules. The remainder *DW* is at rest (it can be detected only in Einsteinian frame K and can be only at rest). The remainder *DR* moves with velocity v and cannot be detected in other Einsteinian reference frames but in frame K’.
Now a question. Can the remainder *DW* in principle be detected in all inertial frames? Yes. It can, if the clocks of all inertial frames are synchronized in "false" non-Einsteinian way so that the processes of burning reach the marks D and W of the rod in all these frames simultaneously.
The one-way speed of light in these non-Einsteinian frames (in Reichenbach's frames) does not equal c. Knowing one-way speed of light the observers of all inertial frames can find the velocity of their proper frames (relative to the frame K). If they will take into account their own speed, then all of them will come to the conclusion that the remainder *DW* is at rest. Likewise, having synchronized the clocks of all inertial frames so that the processes of burning reach the marks D and R of the rod in all these frames simultaneously the observers in all frames will discover that the remainder *DR* is moving with velocity v.
The velocities (and other physical quantities) of the remainder *DW* and *DR* are invariant although it is necessary to do some "tricks" to see the physical objects that we named remainders *DW* and *DR*. Without these "tricks", the observers will not detect these objects, but these objects do exist and should be detectable in all frames of reference.

 

[Ibix]

I don't think anyone disagrees with his analysis. We just don't see the point of it.

 

[A.T.]

I wanted to say, that in Special Relativity observers from different reference frames “see” different physical objects.

According to your definition of "see" and "different". You can make any statement true by appropriately defining the used terms.

 

[Herman Trivilino]

Another observer from another frame sees that one of them is still sucking a pacifier and other one is in a coffin already. I think it is very funny!

If one of the twins is next to me and in a coffin dead at the age of 70 years, and the other twin is 70 light years away, I will see the distant one as a baby. Why is that funny?

On the other hand, if you're thinking of the twin paradox where an observer sees the baby and the old dead twin in the same location at the same time, then all observers will see that same thing. I find that strange, too. Perhaps even funny.

Selection of a frame of reference with respect to which all observers synchronize their clocks brings some order at least.

One can select any frame of reference and do that. Any one inertial reference frame is as good as any other.

Then every observer can see the twins of the same age, 35 years old, healthy with rose cheeks.

If one observer located midway between the twins sees them both at age 35, then all observers at that location regardless of their state of motion sees them both at age 35. It makes no difference how they've synchronized their clocks.

 

[Dale]

I wanted to say, that in Special Relativity observers from different reference frames “see” different physical objects.

Only by your peculiar definition. Your definition is not part of mainstream physics to my knowledge. In my opinion, it is a poor definition, and all of the things that you have said since you came up with this definition are reasons that it is a bad definition.

 

[Bartolomeo]

According to your definition of "see" and "different". You can make any statement true by appropriately defining the used terms.

If one observer located midway between the twins sees them both at age 35, then all observers at that location regardless of their state of motion sees them both at age 35. It makes no difference how they've synchronized their clocks.

Only by your peculiar definition. Your definition is not part of mainstream physics to my knowledge. In my opinion, it is a poor definition, and all of the things that you have said since you came up with this definition are reasons that it is a bad definition.

What kind of definition? I did not make any definitions.

The very first post WITH PICTURES by JesseM. Just think if you change velocity of the moving ruler.
https://www.physicsforums.com/threads/an-illustration-of-relativity-with-rulers-and-clocks.59023/

 

[Bartolomeo]

I don't think anyone disagrees with his analysis. We just don't see the point of it.

They disagree! But you understand relativity of simultaneity. I think so,

 

[Dale]

What kind of definition? I did not make any definitions.

The first 15 posts of this thread were all about getting clarity on your definition of what it means to be the SAME.

This is highly frustrating. If you believe that you are using a standard definition then please provide a reference where being the SAME is defined. Otherwise, please understand that your definition is a personal definition and is one that others may object to.

 

[Ibix]

They disagree! But you understand relativity of simultaneity. I think so,

No one thinks your analysis is wrong. We just have no idea why you are so intent on hiding the principle of relativity under odd synchronisation conventions.

It's like you and the person next to you have drawn graphs of $y=x^2$. You keep pointing out that only one graph is $y=x^2$, and the other is $(y-y_0)\cos\theta_0+(x-x_0)\sin\theta_0=((y-y_0)\sin\theta_0-(x-x_0)\cos\theta_0)^2$. Well, yes, if you insist on everyone using the same coordinate system. But it would be daft to do so. There's no reason to prefer one graph over the other as "actually" passing through the origin, and insisting on the same coordinate system actually obscures that rather useful fact.

That last is why everyone is looking at you in an odd way. We are discussing a theory that is already notoriously difficult to understand, and you seem to be doing your best to hide anything that simplifies it. There can be good reason for doing that but, as Dale points out in his last post, you don't seem to realize that you are doing it.

 

[Bartolomeo]

Only by your peculiar definition. Your definition is not part of mainstream physics to my knowledge. In my opinion, it is a poor definition, and all of the things that you have said since you came up with this definition are reasons that it is a bad definition.

The first 15 posts of this thread were all about getting clarity on your definition of what it means to be the SAME.
This is highly frustrating. If you believe that you are using a standard definition then please provide a reference where being the SAME is defined. Otherwise, please understand that your definition is a personal definition and is one that others may object to.

https://plato.stanford.edu/entries/identity-time/

https://en.wikipedia.org/wiki/Heraclitus#Panta_rhei.2C_.22everything_flows.22

https://en.wikipedia.org/wiki/Identity_(philosophy)

https://en.wikipedia.org/wiki/Law_of_identity

 

[Vanadium 50]

At best, this is philosophy.

 

[Dale]

https://plato.stanford.edu/entries/identity-time/

https://en.wikipedia.org/wiki/Heraclitus#Panta_rhei.2C_.22everything_flows.22

https://en.wikipedia.org/wiki/Identity_(philosophy)

https://en.wikipedia.org/wiki/Law_of_identity

Not a single one of these references uses your definition. Pretending that they do is not conducive to a good discussion.

 

[Herman Trivilino]

Simply posting a list of references with no mention of how they relate to your discussion is also not conducive to a good discussion. Your response to my Post #34 is now the second time you've done this to me: You quote part of my post but don't add any discussion in response to what I'm saying.

In Post #34 I outline a couple of things that appear to be huge misunderstandings on your part. Yet you don't address them.